1. Technical Field
The present invention relates to a method as well as an apparatus for detecting period length fluctuations of a periodic first signal and/or of a periodic second signal, whereby the period length of the second signal is shorter than that of the first signal and a reference number of periods of the second signal, which arise during a certain number of periods of the first signal is obtained.
2. Background Information
In the case of periodic signals disadvantageously fluctuations of the period length also arise. This can lead for example in digital technology to edge-controlled actions being triggered too early or too late causing malfunctions to arise. If for example in the case of serial data communication with data retrieval in a pre-determined cycle the analog value or the digital state of a line must be scanned, period length fluctuations of the scanning rate can lead to errors arising during data retrieval, since scanning is carried out at an incorrect time.
In order to measure the fluctuations of the period length of a periodic first signal, it is known to measure the duration of a period of the first signal several times by means of a periodic second signal, the period length of which is shorter than the period length of the first signal. In this case, a reference number of periods of the second signal, which arise during a period of the first signal and/or can be inscribed in a period is obtained. The period length of the first signal thereby corresponds to the reference number multiplied by the period length of the second signal. In this case, a quantization error arises, since the period length of the first signal is only resolved with an integral number of periods of the second signal, the quantization error falling with decreasing period length of the second signal. In addition, period length fluctuations of the second signal also have an effect on the measurement, whereby in relation to the second signal, the accumulated period length fluctuations make it possible to realize that in a measurement period the period length fluctuations of the reference number are added onto periods of the second signal. The period length fluctuations of the second signal therefore have a greater effect on the measurement result, the higher the reference number.
FIG. 1 illustrates the basic principle of this measurement process. In this case, a reference number m is defined in periods of the second signal 2, which can be inscribed in a period of the first signal 1. The period length of the first signal 1 is provided with the reference symbol 3 and features period length fluctuations, which are shown as broken lines. In known methods, in order to detect the period length fluctuations of the first signal 1, a signal 2 with very short period length fluctuations is used, so that the period length of individual periods of the first signal 1 can be measured with high precision. Vice-versa if the signal 1 is present with high precision and very short period length fluctuations, the accumulated or added period length fluctuations of the second signal can be detected. By multiple measurements of reference numbers m, the period length fluctuations of the first signal or the accumulated period length fluctuations of the second signal can therefore be measured, dependent on what signal with high precision and/or with short period fluctuations is present.
Disadvantageously, however, this requires at least a high precision signal with a very short period length fluctuation.